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Tim Williams[_3_] Tim Williams[_3_] is offline
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Default Tube mono-block amp with SIX 6L6 outut tubes

"Big Bad Bob" wrote in message
...
I think it works ok without "all that". fuses where needed of course, to
avoid things catching on fire. But tubes are amazingly strong at
absorbing conditions that transistors would melt under. Sure the plates
turn pink [like when half of a push-pull transformer melts away] but if
you don't push them to the edge of physics they generally take it ok and
survive getting a new output transformer.


A lot of sweep tube datasheets contain the rating, "short term overload
duration: 220W for 60s" or something like that. Transistors can only dream
of such abuse, gone in milliseconds!

But the purpose of that rating must be understood. These were TV tubes, and
the sweep tube in particular often took a beating as other tubes heated up
and other signals stabilized: horizontal oscillator and sync, and the damper
diode especially -- its high cathode voltage isolation takes a long time to
warm up.

There was definitely no money in adding a protection circuit! Burn a tube,
pop it out, take it down to the corner drugstore and buy a new one for a
buck or a few.

Nowadays, with both tubes and transformers being rather pricey, let alone
the repairman -- the balance changes, and especially with how little
hardware is involved in adding a protection circuit (if one does not mind
that it contains silicon), it's well worth it.

Tim

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Seven Transistor Labs, LLC
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